The present invention relates to a system and method for automatically controlling the cruising speed of a vehicle so as to maintain the vehicle speed at a desired cruising speed.
A Japanese Patent Application first publication Sho 60-163735 published on Aug. 26, 1985 exemplifies one such cruising speed controlling system for vehicles.
The disclosed cruising speed controlling system includes a controller, a power supply of which is supplied from a vehicle battery via an ignition switch and main switch. The controller includes a power supply regulator receiving a power supply voltage from the vehicle battery via the main switch and maintaining the power supply voltage at a constant voltage required to operate a microcomputer. The microcomputer includes a CPU (Central Processing Unit), Input Port, Output Port, ROM (Read Only Memory) which permanently stores a control program, RAM which temporarily stores operating variables for settling an opening angle of a throttle valve (to be described later), and a bus line. It should be noted that ROM receives its power supply voltage from the vehicle battery via another power supply circuit to prevent erasure of the contents of the ROM.
The Input Port is connected to both a vehicle speed sensor 12 and a command switch used to control the cruising speed.
The command switch includes a set switch through which the cruising speed control for the vehicle to automatically run at a constant speed is commanded, an accelerator switch through which a constant acceleration control for the vehicle to automatically accelerate at a constant rate is commanded, and a resume switch (reset switch) through which a recovery of the vehicle speed to a stored vehicle cruising speed is commanded.
On the other hand, the output port of the controller is connected to a relay and an actuator.
When the relay receives the power supply and the relay contact is closed, the actuator receives the power supply. The actuator includes a ventilation valve, safety valve, and vacuum supply valve. When the vacuum valve is open and simultaneously the ventilation valve and safety valve are closed, negative pressure is introduced into a negative pressure chamber so that a throttle valve of a vehicular engine is actuated in an open direction. On the other hand, when the ventilation valve is opened with the vacuum valve and safety valve simultaneously closed, atmospheric pressure is introduced into the negative pressure chamber so that the throttle valve is actuated in a closed direction.
Furthermore, in a power supply line between the relay and main switch, a brake switch which is opened when a brake operation through a brake pedal is carried out and a clutch switch which is opened when a clutch of a vehicular transmission is operated are installed.
During the cruising speed control, the power supply to the relay is interrupted when a brake pedal is depressed and/or when a clutch pedal is depressed. Therefore, the actuation of the throttle valve through the actuator is released.
In addition, a set signal, generated when a switch of a stop lamp which is lighted when the brake pedal is depressed, is supplied to the input port of the microcomputer to release the cruising speed control for the controller.
In the cruising speed controlling system disclosed, e.g., in the above-identified Japanese Patent Application publication, a first initialize signal to be supplied to the actuator is set to prevent a drop of the vehicle speed immediately after the accelerator switch is operated, a tap-up initialize signal to be supplied to the actuator is set to make a minute speed increase of the vehicle speed when the accelerator switch is operated after the constant acceleration control is ended in response to non-operation of the accelerator switch, and a small initialize signal to be supplied to the actuator is set to improve speed adjustment characteristics during the acceleration occurring while the accelerator switch is again operated.
However, since in the cruising speed controlling apparatus for the vehicle one of the initialize signals has no correlation to the other initialize signals and they have mutually different constant values, and they are set to constant values irrespective of the vehicle speed, the constant values thereof need to be determined after tuning is carried out whenever the systems are installed in the vehicles in order to adjust them to a plurality of different vehicle models having different power demands. Consequently, the operations for installation of the system in each vehicle is troublesome and installation costs are increased. In addition, since each initialize signal is not set to an appropriate value according to the vehicle speed, it is difficult for the response characteristics at low vehicle speeds and at a high vehicle speeds to become compatible.